From: Kaartic Sivaraam <kaarticsivaraam91196@gmail.com>
To: Michael Haggerty <mhagger@alum.mit.edu>,
Jonathan Nieder <jrnieder@gmail.com>
Cc: Junio C Hamano <gitster@pobox.com>,
Alex Riesen <raa.lkml@gmail.com>,
git@vger.kernel.org
Subject: Re: [PATCH] for_each_string_list_item(): behave correctly for empty list
Date: Tue, 19 Sep 2017 20:08:06 +0530 [thread overview]
Message-ID: <b03c7b09-853f-a2ed-f73e-7d946c90cedb@gmail.com> (raw)
In-Reply-To: <b8951886-feab-a87a-9683-3c155cfa98a8@alum.mit.edu>
On Saturday 16 September 2017 09:36 AM, Michael Haggerty wrote:
>> Does the following alternate fix work? I think I prefer it because
>> it doesn't require introducing a new global. [...]
>> #define for_each_string_list_item(item,list) \
>> - for (item = (list)->items; item < (list)->items + (list)->nr; ++item)
>> + for (item = (list)->items; \
>> + (list)->items && item < (list)->items + (list)->nr; \
>> + ++item)
> This is the possibility that I was referring to as "add[ing] overhead to
> each iteration of the loop". I'd rather not add an extra test-and-branch
> to every iteration of a loop in which `list->items` is *not* NULL, which
> your solution appears to do. Or are compilers routinely able to optimize
> the check out?
It seems at least 'gcc' is able to optimize this out even with a -O1
and 'clang' optimizes this out with a -O2. Taking a sneak peek at
the 'Makefile' shows that our default is -O2.
For a proof, see https://godbolt.org/g/CPt73L
---
Kaartic
next prev parent reply other threads:[~2017-09-19 14:38 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-15 16:00 [PATCH] for_each_string_list_item(): behave correctly for empty list Michael Haggerty
2017-09-15 18:43 ` Jonathan Nieder
2017-09-16 4:06 ` Michael Haggerty
2017-09-16 11:51 ` SZEDER Gábor
2017-09-17 10:19 ` Michael Haggerty
2017-09-19 14:38 ` Kaartic Sivaraam [this message]
2017-09-20 1:38 ` Junio C Hamano
2017-09-20 1:43 ` Jonathan Nieder
2017-09-20 5:14 ` Junio C Hamano
2017-09-20 2:30 ` Jonathan Nieder
2017-09-20 3:54 ` Junio C Hamano
2017-09-20 5:27 ` [PATCH v2] for_each_string_list_item: avoid undefined behavior " Jonathan Nieder
2017-09-20 5:40 ` Junio C Hamano
2017-09-20 7:00 ` Michael Haggerty
2017-09-20 7:40 ` Kaartic Sivaraam
2017-09-20 12:22 ` [PATCH v2] doc: camelCase the config variables to improve readability Kaartic Sivaraam
2017-09-20 16:28 ` [PATCH v2] for_each_string_list_item: avoid undefined behavior for empty list Andreas Schwab
2017-09-20 17:31 ` Jonathan Nieder
2017-09-20 21:51 ` Andreas Schwab
2017-09-21 1:12 ` Junio C Hamano
2017-09-21 15:39 ` Andreas Schwab
2017-09-20 7:35 ` [PATCH] for_each_string_list_item(): behave correctly " Kaartic Sivaraam
2017-09-17 0:59 ` Junio C Hamano
2017-09-17 10:24 ` Michael Haggerty
2017-09-18 0:37 ` Junio C Hamano
2017-09-19 0:08 ` Stefan Beller
2017-09-19 6:51 ` Michael Haggerty
2017-09-19 13:38 ` SZEDER Gábor
2017-09-19 13:45 ` SZEDER Gábor
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